Pursuant to a demand for high-class pleasant houses, a natural marble is recently spotlighted as a building material. Despite the high surface hardness and graceful texture thereof, the natural marble fails to be popularized because it is high-priced, heavyweight and weak in impact resistance.
In contrast, an artificial marble developed as an alternative to the natural marble is capable of realizing many different patterns and is quite glossy, highly resistant to severe temperature change, low in moisture absorbency and high in strength. Thus, the artificial marble can provide excellent decoration effects when applied to high-class houses, hotels, apartments and so forth. This leads to a sharp increase in demand over the world.
In general, the artificial marble is produced by mixing a filler material such as natural stone powder or synthetic inorganic material powder with a resin and press-forming the mixture with a vacuum compression press or molding the mixture with a mold. Examples of the filler material include marble chips made from aluminum hydroxide, barium sulfate, magnesium sulfate, barium carbonate, calcium carbonate, silica, granite and other inorganic materials. Examples of the resin include syrup prepared by melting a thermosetting unsaturated polyester resin or a thermoplastic polymethyl methacrylate (PMMA) resin in methylmethacrylate monomers.
In order for the artificial marble to have many different colors and patterns, the marble chips are produced by adding pigments or other additives to a resin, curing the mixture into a thick plate shape and crushing the plate into chips with different sizes.
The term “artificial marble” refers generally to artificially synthesized products with texture like a natural marble, which is produced by mixing natural stone powder or mineral powder with a resin, such as acryl, unsaturated polyester or epoxy, or a cement and adding pigments and other additives to the mixture. Depending on the kind of the forming method or the kind of matrix, the artificial marble is largely classified into an acryl-based artificial marble, an unsaturated polyester-based artificial marble, an epoxy-based artificial marble and an engineered stone-based artificial marble.
Among them, the engineered stone-based artificial marble is most similar in texture to a natural marble and is made from a main component such as natural stone powder, quartz, glass, mirror or aluminum hydroxide and 15 wt % or less of binder resin. The engineered stone-based artificial marble is similar in color and texture to the natural marble and, therefore, is popularly used as an alternative to the natural marble. However, the engineered stone-based artificial marble has a drawback in that it is high in specific gravity and hard to process. As compared with the acryl-based artificial marble or the unsaturated polyester-based artificial marble, it is hard to use the engineered stone-based artificial marble as a general-purpose building material.
As a solution to this problem, certain artificial marble manufacturers make an attempt to develop marble chips with high specific gravity and high transparency, thereby giving the texture of natural marble to the acryl-based artificial marble.
Korean Patent Laid-open Publication No. 10-2007-0115350 discloses a method of producing multi-layered marble chips by forming an inorganic material layer with high specific gravity on a layer with low specific gravity. The marble chips thus produced are useful as high-specific-gravity marble chips but are incapable of realizing complete transparency.
Korean Patent Registered Publication No. 10-0750514 discloses halogenated epoxy acrylate marble chips superior in transparency and specific gravity. However, the marble chips are weak in impact resistance and likely to become yellowish due to the degradation in the manufacturing process. Since the resin composition for the manufacture of the marble chips contains acrylic acid, it becomes yellowish over time.